1. Field of the Invention
The present invention relates to a method of producing a micro structure using a micro mechanics, particularly to a method of producing a micro structure using electroplating, a method of producing a liquid discharge head, a liquid discharge head produced thereby, a head cartridge loaded with said liquid discharge head, and a device for discharging liquid produced therewith.
2. Related Background Art
In recent years, a micro machine having a small movable mechanism has been investigated by using micro mechanics techniques. Especially, a micro structure produced by using a semiconductor integrated circuit production technique (semiconductor photo lithography process) makes it possible to produce on a substrate a plurality of micro machine parts which are more miniaturized and highly reproductive. Accordingly, this provides relatively easier arraying and lower production costs, in addition, with such miniaturization, and more rapid responsibility can be expected as compared with conventional mechanical structures.
Of the micro mechanics techniques using a semiconductor photo lithography process, surface micro-machining which uses a sacrifice layer is a method in which micro structures such as a micro cantilever, a linear actuator or the like can be easily made on a substrate, and various devices have been developed using this process.
Two typical surface micro-machining methods which use a sacrifice layer will be described below.
A first surface micro-machining method is such that a poly silicon film or an SOI (Si on Insulator) film, formed into a thin layer through a silicon dioxide film on a silicon substrate, which is to become a micro structure is patterned in a desired shape and then the oxidizing film of silicon dioxide is removed with an aqueous solution of hydrofluoric acid. With this method, a linear actuator (D. Kobayashi et al., xe2x80x9cAn Integrated Lateral Tunneling Unit,xe2x80x9d Proceedings of IEEE Micro Electro Mechanical Systems Workshop 1992, pp.214-219) or the like can be manufactured. In this method, a sacrifice layer for use in producing micro structures is a single layer common to all of the structures.
FIGS. 5A to 5E are diagrammatic illustrations of the production process of micro structures using this method. First, a silicon dioxide film 511 as a sacrifice layer, a poly silicon film 513 as a structure layer and a nickel mask layer 514 are formed on a substrate 512 in this order (FIG. 5A). The nickel mask layer 514 is then patterned, and using this as a mask, the poly silicon film 513 is etched to produce micro structures A, B and C comprising the poly silicon film 513 (FIG. 5B). After this, the nickel mask layer 514 is removed to allow the poly silicon film 513 to be exposed (FIG. 5C), then the silicon dioxide film 511 is etched with an aqueous solution of hydrofluoric acid. This produces a void below the central micro structure B, as shown in FIG. 5D. And in the micro structures A and C on both sides of the micro structure B, the silicon dioxide film 511 which supports both A and C is side-etched to have a cantilever shape. Lastly, a metal film 515 which is a laminate of Cr and Au in this order is deposited on the surface of each of the structures A, B and C so as to produce electrically conductive micro structures A, B and C (FIG. 5E).
A second surface micro-machining method is such that micro structures are produced on the sacrifice layer, which has been formed into a desired pattern, by the thin-film formation process. With this method, a wharve micro motor (M. Mehregany et al., xe2x80x9cOperation of microfabricated harmonic and ordinary side-drive motors,xe2x80x9d Proceedings IEEE Micro Electro Mechanical Systems Workshop 1990, pp.1 to 8), a cantilever (L. C. Kong et al., Integrated electrostatically resonant scan tip for an atomic force microscopexe2x80x9d J. Vac. Sci. Technol. Bll(3), p.634, 1993) or the like can be produced.
FIGS. 6A to 6D illustrate the production process of a cantilever using this method. First, a sacrifice film layer 611 is formed on a silicon substrate 612 having a passivation layer 614 formed on it, after which the sacrifice layer 611 is patterned by using semiconductor photo lithography techniques and etching (FIG. 6A). A structure layer 613, which is to become micro structures, is then formed on the substrate 612 (FIG. 6B), and the structure layer 613 is patterned to have a desired shape using semiconductor photo lithography techniques and etching (FIG. 6C). Then the sacrifice layer 611 is etched with an etchant capable of removing the sacrifice layer 611 alone so as to produce a cantilever 612 shown in FIG. 6D. With this method, more complicated structures can be produced by forming a plurality of sacrifice layers and structure layers. (L. Y. Lin et al., xe2x80x9cMicromachined Integrated Optics for Free-Space Interconnections,xe2x80x9d Proceedings of IEEE Micro Electro Mechanical Systems Workshop 1995, pp.77 to 82).
The conventional methods of producing a micro structure mentioned above, however, have problems as follows.
First, in the first method shown in FIGS. 5A to 5E, the length of the micro structures A and C on both sides depends on the etching conditions of the silicon dioxide film 511, therefore the varying concentration, temperature and agitation of etching reagent may cause its variation. The variation of the length of a micro structure results in variation of mechanical properties, such as spring constant, resonance frequency, etc., of the cantilever and joist or the like which are connected to the structure. Thus, this method leads to a reduction in reproductivity of micro structures.
On the other hand, when the displacement of a cantilever is caused by external force, the stress typically concentrates on the base of the cantilever. In case of the cantilever 621 produced in the manner shown in FIGS. 6A to 6D, the stress concentrates on an inflection portion 622. The substrate bottom side of such an inflection portion becomes a concentration part of the stress D which is excessively strained, therefore deterioration in its mechanical strength with time tends to occur at that portion, which allows its breaking due to mechanical metal fatigue to easily occur.
The present invention has been made in light of such difficulties the foregoing prior arts have, and therefore, the object of the present invention is to provide a method of producing a micro structure of which
(1) variation in mechanical properties is small, and
(2) deterioration in its mechanical strength with time due to the stress concentration at the inflection portion can be controlled.
In order to attain the above object, one aspect of the present invention provides a method of producing a micro structure on a substrate which has a support portion and a plate-like portion supported thereby at a distance from the substrate, comprising the steps of:
forming a spacer layer consisting of an insulating material on a substrate having an electrically conductive layer formed on its surface,
forming a latent image layer consisting of an electrically conductive material on the spacer layer at a site where the plate-like portion of a structure is to be formed,
producing an aperture, where a part of the electrically conductive layer is exposed, on the spacer layer at a site where the supporting portion of a structure is to be formed,
forming a structure layer consisting of plating film inside of the aperture and on the latent image layer by electroplating the electrically conductive layer as a cathode, and
removing the spacer layer.
Another aspect of the present invention provides a method of producing a liquid discharge head for discharging liquid from a discharge port, wherein the liquid discharge head has at least a discharge port for discharging liquid, a liquid flow path in communication with the discharge port for supplying the liquid to the discharge port, a substrate provided with a heating element for allowing the liquid filled in the liquid flow path to generate bubble, and a movable member supported by and fixed to the substrate at a position apart from the substrate and opposite to the heating elements with its free end toward the discharge port, and the liquid discharge head discharges the liquid from the discharge port by having the free end of the movable member displaced toward the discharge port around a supporting point constructed in the neighborhood of the portion where the movable member is supported by and fixed to the substrate by pressure generated by the bubble generation, characterized in that the method comprises the steps of:
forming an electrically conductive layer consisting of an electrically conductive material on the top layer of the substrate,
forming a spacer layer for making the void on the electrically conductive layer,
forming a latent image layer consisting of an electrically conductive material on the spacer layer so that the latent image layer can have almost the same shape as the movable member,
removing a portion of the spacer layer corresponding to the portion where the movable member is supported and fixed, so as to expose a part of the electrically conductive layer so as to form an aperture on the more upstream side of the liquid flow path, in terms of liquid flow direction, relative to the latent image layer,
forming a metal plating layer constituting the movable member on the electrically conductive layer as well as on the latent image layer by electroplating using the electrically conductive layer as a cathode, and
forming the movable member by removing the spacer layer.
Further, another aspect of the invention provides a liquid discharge head, wherein the liquid discharge head has at least a discharge port for discharging liquid, a liquid flow path in communication with the discharge port for supplying the liquid to the discharge port, a substrate provided with a heating element for allowing the liquid filled in the liquid flow path to generate bubble, and a movable member supported by and fixed to the substrate at a position apart from the substrate and opposite to the heating element with its free end toward the discharge port, and the liquid discharge head discharges the liquid from the discharge port by having the free end of the movable member displaced toward the discharge port around a supporting point constructed in the neighborhood of the portion where the movable member is supported by and fixed to the substrate by pressure generated by the bubble generation, characterized in that the liquid discharge head is produced by the method comprises the steps of:
forming an electrically conductive layer consisting of an electrically conductive material on the top layer of the substrate,
forming a spacer layer for making the void on the electrically conductive layer,
forming a latent image layer consisting of an electrically conductive material on the spacer layer so that the latent image layer can have almost the same shape as the movable member,
removing a portion of the spacer layer corresponding to the portion where the movable member is supported and fixed, so as to expose a part of the electrically conductive layer so as to form an aperture on the more upstream side of the liquid flow path, in terms of liquid flow direction, relative to the latent image layer,
forming a metal plating layer constituting the movable member on the electrically conductive layer as well as on the latent image layer by electroplating using the electrically conductive layer as a cathode, and
forming the movable member by removing the spacer layer.
According to the present invention, as described above, a structure having a supporting portion and a plate-like portion is formed of a plating film deposited and developed on an electrode and a latent image layer, wherein, since the plate-like portion of the micro structure is formed of the plating film deposited and developed on the latent image layer, and after forming a structure layer of the plating film, the entire spacer layer is removed, the size of the plate-like portion is defined by the size of the latent image layer. Accordingly, unlike the conventional methods in which a plate-like portion is formed by etching and removing a structure layer immediately under the member which is to become the plate-like portion, the length of the plate-like portion does not vary with the etching conditions. In addition, since the supporting portion of the micro structure is formed of a metal plating layer deposited and developed within the aperture provided on the spacer layer, the size of the supporting portion can be set independent of the thickness of the plate-like portion. As a result, if the size of the aperture portion is allowed to be larger relative to the thickness of the plate-like portion of a structure to be made, the stress concentration applied to the base of the plate-like portion will be relieved. The simplest structure made according to the present invention is, for example, a cantilever which is supported on a substrate by a supporting portion.
Further, a micro structure provided with an aperture in its plate-like portion can be also made by adding to the method a step of forming a second spacer layer at one site of the latent image layer to produce a structural layer, wherein a plating film is developed to a height with which it can surround the second spacer layer. In this case, if an opening is provided for the first spacer layer in the zone surrounding the latent image layer, a hollow micro structure having an opening provided on its top surface can be made. Still further, if another step is added to the above method at which one site of the substrate is removed from its bottom side so as to expose one site of the first spacer layer formed on the electrode, a nozzle structure can be made which is provided with a site removed from the substrate as a liquid supply opening and an opening on its top surface as an injection opening.
Further, if a plurality of latent image layers are formed leaving a space between each other, a plating film is deposited and developed on the layers in the order of increasing distance from the opening portion of the spacer layer. This provides a plate-like portion of which thickness changes in multiple different levels. Although the micro structure made still has a latent image layer on the back of the plate-like portion, the latent image can be removed after making a structural layer, if it is unnecessary.
The above spacer layer can be formed of high polymer resin. In this case, preferably oxygen plasma is used to remove the spacer layer, since it can easily peel the layer.
According to the present invention, on the spacer layer, a latent image layer is formed of an electrically conductive material in the shape of a movable member, and on the latent image layer, a metal plating layer which is to be the movable member is deposited and formed by electroplating. This allows to form a movable member with a high accuracy and high density, and consequently, to produce a liquid discharge head or the like which is stable in its discharge property in discharging liquid and highly reliable.